VXLAN and BGP EVPN Configuration Guide for Dell EMC SmartFabric OS10 Release 10.5.2

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Example: Migrating from Asymmetric IRB to Symmetric IRB

Until Release 10.5.0, OS10 provided support only for the Asymmetric IRB mode. Starting from Release 10.5.1, OS10 supports the Symmetric IRB mode. Symmetric IRB mode efficiently uses next hop tables in the NPU. If there are no local hosts, Symmetric IRB mode does not require creation of destination VNI in the local VTEP. You can migrate your network from Asymmetric IRB mode to Symmetric IRB mode. For a seamless migration with less or no downtime in the VLT environment, perform the following steps:

NOTE
  • Before you start this migration, all leaf nodes acting as VTEPs in the Clos network must be upgraded to 10.5.1.x.
  • If there are overlay hosts in default VRF, migration to Symmetric IRB mode is not supported because Symmetric IRB mode cannot be used in default VRF.
Migrating from Asymmetric IRB to Symmetric IRB

Asymmetric to Symmetric IRB migration steps

  1. Make the spines to send overlay traffic only to Leaf-2 by making Leaf-1 advertise VTEP IP with a higher metric in the underlay network.

    Leaf-1 configuration

    1. Configure route-map with prefix-list to set the metric higher for the VTEP IP.
      Leaf-1(config)# ip prefix-list vtep_ip seq 10 permit 10.10.10.1/32
      Leaf-1(config)# route-map set_higher_metric permit 10
      Leaf-1(config-route-map)# match ip address prefix-list vtep_ip
      Leaf-1(config-route-map)# continue 20
      Leaf-1(config-route-map)# set metric 100
      Leaf-1(config-route-map)# exit
      Leaf-1(config)# route-map set_higher_metric permit 20
      Leaf-1(config-route-map)# exit
      
    2. Configure the route-map to the underlay BGP neighbors towards Spine.
      Leaf-1(config)# router bgp 65100
      Leaf-1(config-router-bgp-65100)# neighbor 10.1.1.1
      Leaf-1(config-router-neighbor)# address-family ipv4 unicast
      Leaf-1(config-router-bgp-neighbor-af)# route-map set_higher_metric out
      Leaf-1(config-router-bgp-neighbor-af)# exit
      Leaf-1(config-router-neighbor)# exit
      Leaf-1(config-router-bgp-65100)# neighbor 10.2.1.1
      Leaf-1(config-router-neighbor)# address-family ipv4 unicast
      Leaf-1(config-router-bgp-neighbor-af)# route-map set_higher_metric out
      Leaf-1(config-router-bgp-neighbor-af)# end
      
  2. Spines would now send the overlay traffic destined to VLT domain 1 (Rack1) only to Leaf-2.
  3. Configure Symmetric IRB mode in Leaf-2.

    Leaf-2 configuration

    1. Configure router-mac.
      Leaf-2(config)# evpn
      Leaf-2(config-evpn)# router-mac 02:10:10:10:10:10
      
    2. Configure IP VRF with L3 VNI.
      Leaf-2(config-evpn)# vrf BLUE
      Leaf-2(config-evpn-vrf-VRF001)# vni 65001
      
    3. Configure RT (auto or manual) and RD (optional, default is auto).
      Leaf-2(config-evpn-vrf-BLUE)# route-target auto
    4. Advertise IPv4 and IPv6 connected routes.
      Leaf-2(config-evpn-vrf-BLUE)# advertise ipv4 connected
      Leaf-2(config-evpn-vrf-BLUE)# advertise ipv6 connected
      
  4. Leaf-2 is changed to Symmetric IRB mode. VTEPs in other racks could be using Symmetric IRB or Asymmetric IRB based on its own local configuration. Irrespective of what other remote VTEPs use, Leaf-2 could now handle VXLAN encapsulated traffic from both symmetric and asymmetric modes.
  5. Configure Symmetric IRB in Leaf-1.

    Leaf-1 configuration

    1. Configure router-mac.
      Leaf-1(config)# evpn
      Leaf-1(config-evpn)# router-mac 02:10:10:10:10:10
      
    2. Configure IP VRF with L3 VNI.
      Leaf-1(config-evpn)# vrf BLUE
      Leaf-1(config-evpn-vrf-VRF001)# vni 65001
      
    3. Configure RT (auto or manual) and RD (optional, default is auto).
      Leaf-1(config-evpn-vrf-BLUE)# route-target auto
    4. Advertise IPv4 and IPv6 connected routes.
      Leaf-1(config-evpn-vrf-BLUE)# advertise ipv4 connected
      Leaf-1(config-evpn-vrf-BLUE)# advertise ipv6 connected
      
  6. Remove the BGP MED configuration in Leaf-1. Spines start sending traffic to Leaf-1 as well. ECMP path from Spines towards Leaf-1 and Leaf-2 is restored.

    Leaf-1 configuration

    Leaf-1(config)# router bgp 65100
    Leaf-1(config-router-bgp-65100)# neighbor 10.1.1.1
    Leaf-1(config-router-neighbor)# address-family ipv4 unicast
    Leaf-1(config-router-bgp-neighbor-af)# no route-map set_higher_metric out
    Leaf-1(config-router-bgp-neighbor-af)# exit
    Leaf-1(config-router-neighbor)# exit
    Leaf-1(config-router-bgp-65100)# neighbor 10.2.1.1
    Leaf-1(config-router-neighbor)# address-family ipv4 unicast
    Leaf-1(config-router-bgp-neighbor-af)# no route-map set_higher_metric out
    Leaf-1(config-router-bgp-neighbor-af)# end
    
  7. Rack1 is migrated to use Symmetric IRB.
  8. Repeat Steps 1-to-6 on Rack2 and other racks as well.
  9. After changing all Racks to Symmetric IRB, you can perform the following optional configuration changes:
    1. If the L2 VNI (MAC-VRF VNI) does not have local hosts in the VTEPs, you can remove those VNIs on those VTEPs.
    2. Default route configured in VTEPs pointing to border leaf using an intermediate VNI could be removed. Default route or external routes could now be advertised to the VTEPs from border leaf using advertise commands under EVPN-IP-VRF mode.

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